It is already known that a step-change in torque generally occurs when switching over between two modes of operation, and that depending on the mode of operation this can be impermissibly large. The reason for this step-change in torque is evidently that the magnitudes of the air masses inducted into the cylinders of the internal combustion engine differ for the different modes of operation, generating torques with a corresponding magnitude. The step-change in torque can lead to irregular running of the internal combustion engine, which makes itself evident in driving use in undesirable ways, for example as juddering.
In the case of small step-changes in the air masses it has been possible, until now, to compensate for them by resetting of the ignition angle. This involves retarding the ignition angle far enough to ensure reliable combustion of the fuel-air mixture. However, the late combustion of the fuel-air mixture effects a reduction in the torque. With a large step-change in the air mass, the situation could arise in which a resetting of the ignition angle alone is no longer sufficient to compensate for the step-change in torque. To avoid undesirable juddering of the vehicle occurring in this case, the switchover to the second mode of operation is generally inhibited, or the engine is so arranged that no large step-change can occur in the air mass. The price for this is a correspondingly higher fuel consumption.